High gain two bay unidirectional broadband antenna

ABSTRACT

A unidirectional broadband horizontally polarized HF two bay antenna with an upper bay and a lower bay using a larger Alpha angle than the upper bay. Both bays also employ substantially the same Tau ratio even though the bay Alpha angles are different. These result in an optimized antenna structure of minimum size for the frequency range of operation, and with resultant points of equal radiated phase from the two bays lying substantially in a vertical line for any one particular operational frequency.

[ 51 Oct. 3, 1972 United States Patent Cory et al.

[54] HIGH GAIN TWO BAY Primary ExaminerEli Lieberman UNIDIRECTIONALBROADBAND Attorney-Warren H. Kintzinger and Robert J. Craw- ANTENNA ford[72] Inventors: Terry S. Cory; Roger A. Markley,

[57] ABSTRACT A unidirectional broadband horizontally polarized HF twobay antenna with an upper bay and a lower bay using a larger 0: anglethan the upper bay. Both bays both of Richardson, Tex.

[73] Assignee: Collins Radio Company, Dallas,

Tex.

221 Filed: May 25,1971

21 Appl.No.: 146,764

also employ substantially the same 1' ratio even though the bay 0:angles are different. These result in an optimized antenna structure ofminimum size for the frequency range of operation, and with resultant gmm""mm343/792'5 256 Points of equal radiated phase from the two bayslying substantially in a vertical line for any one particularoperational frequency.

[58] Field of Search....343/792.5, 811

Reierences Cited UNITED STATES PATENTS 14 Claims, 16 Drawing Figures3,271,774 9/1966 Justice....................343/7925 PAR PATENTEDHBIEII972 3.696.430

sum 1 OF 7 TERRY S. OORY ROGER A. MARKLEY BY M ATTORNE PKTENTED m 3 I973INVENTORS TERRY 3. com ROGER A. MARKLEY Wm ATTO NEY PATENTEM I9733.698430 TERRY S. CORY ROGER A. MARKLEY BY 7/ ATI E NEY PATENTEDnma 19123.6963430 SHEEI 5 0F 7 FlG. 8

REFLECTION AREA RADIATING ELEMENT 8 w FlG. 9

INVENTORS TERRY S. CORY ROGER A. MARKLEY ATTORKIEY PATENTEDUCT 3 1972SHEET 6 OF 7 s 4 m 2 T V v m m 2 2 A m /l F \V w FREQUENCY IN MHZ OTERRY S. CORY BY ROGER A. MARKLEY IV Afl NEa 7 20.5 MHz PATENTEDnc-m m23,696,430

sum 1 or 7 IN VENTORS TERRY S. C ROGER A. MARKL BY m ATTORNEY HIGH GAINTWO BAY UNIDIRECTIONAL BROADBAND ANTENNA This invention relates ingeneral to antenna systems and, in particular, to a horizontallypolarized high gain two bay unidirectional broadband HF antenna using alarger angle for the lower bay than for the upper bay.

Pre-existing two bay log periodic and horizontally polarized HF antennaswith similar radiation characteristics to applicants present antennagenerally require towers much higher than the maximum height of the rearlowest frequency radiating elements. The use of equal length upper andlower bays results in the longest dimension of the bays, measured from acommon apex, lying on the arc of a circle with a center at the commonapex. These prior art antennas, having upper and lower bays constructedwith identical log periodic parameters, have radiation phase centerslying substantially on circular arcs measured from the common apex ofthe antenna. With some two bay broadband HF antennas excitation phasedifference has been accomplished to some degree with log periodicscaling that increases the physical size of the lower bay with respectto the upper bay. This, however, further compounds size difficultiespointed out hereinbefore with respect to tower size required forsupporting bays arranged physically on circular arcs from an antennacommon apex or projected apex substantially on the ground. This meansthat with many of these structures that the lower phase center is closerto any vertical line to the rear of the array than is the upper phasecenter for the upper bay. If the vertical line mentioned represents oneof the rear supporting towers for the antenna, the tower height is givenby X sine A where A is the angle of the upper bay curtain with respectto ground and X is the distance that the tower is located away from theapex. For a fixed A, X is determined by the lower bay curtain because ofits smaller angle with respect to the ground. Scaling the lower elementsto obtain phase shift has the effect of increasing the tower height evenmore as pointed out hereinabove. It is obvious, then, that if thecurtains or bays could be designed so as to position the phase centersand elements of equal length of the curtains in a vertical line; i.e.,directly above and below one another, X would be a lesser distance andthe required tower height would be less and essentially determined bythe length of the upper curtain only. This is not exactly the case,however, since factors such as constant factor due to mutual couplingbut it is quite close to actual conditions. The actual lower bay,designed by using different a angles, is short of reaching the reartower; a facet which aids in achieving improved performance with smalleroverall antenna size when the proper phasing is achieved.

It is, therefore, a principal object of this invention to provide a highgain two bay unidirectional HF broad band antenna capable of producingmaximum power gain from an antenna of minimum size for a specificradiation beam maximum angle through a predetermined HF frequency rangeof operation.

Another object is, with respect to any particular frequency throughoutthe range of operational frequencies, for points of equal radiated phasefrom the two bays to be in substantially vertical alignment and todevelop a radiated field vertical phase front.

A further object is to achieve a balanced transmission line feed to theupper and lower antenna bays in the sense that no unbalanced feed systemcurrent flow occurs in any ground leads that would either upset theantenna impedance or shunt any radiated power into ground. This isachieved with a balanced transmission line feed to the antenna bayshaving different a angles since the bays are not perfect geometriccomplements of one another.

Features of the invention useful in accomplishing the above objectsinclude, in a high gain two bay unidirectional broadband HF antenna atwo bay array of two horizontally polarized log-periodic curtainsdesigned and arranged in a manner such that maximum gain is achieved fora given size. The two curtains are stacked vertically and arrayed withrespect to the common apex on the ground. Actually, the curtains of thetwo bays are truncated arbitrarily with a feed system including anunbalanced coax line feeding a balun having a balanced transmission lineoutput connection to the two bays of the antenna with the lowest portionof the balun being approximately 9 feet above ground.

A specific embodiment representing what is presently regarded as thebest mode of carrying out the invention is illustrated in theaccompanying drawings.

FIG. 1 represents a perspective of applicants high gain two bayunidirectional broadband HF antenna;

FIG. 2, a horizontal plan projection of the two bay antenna of FIG. 1;

FIG. 3, a side elevation view of the antenna of Fig. 1;

FIG. 4, a partial side elevation view showing feed detail;

FIG. 5, a perspective view of the unbalanced coaxial line input to twosided balanced transmission line output balun with the two balancedtransmission lines sides feeding the upper and lower bays of theantenna;

FIGS. 6 and 7, plan views of the lower and upper bay curtains,respectively;

FIG. 8, a side elevation showing of the direct and reflected radiationemanating from a radiating element (or tuned frequency activated zone ofthe antenna);

FIG. 9, a horizontal plan view of a radiating element and the groundreflection area therefor;

FIG. 10, a VSWR to frequency in MHz diagram for the antenna;

FIGS. 11, 12, and 13, elevation H-plane patterns for the antenna at 8MHz, 16 MHz, and 20.5 MHz respectively; and

FIGS. 14, 15, and 16, azimuth E-plane voltage patterns for the antennaat 8 MHz, 13 MHz, and 22.5 MHz, respectively.

The horizontally polarized unidirectional broadband HF antenna 20 ofFIG. 1 is shown to be a two bay array of two horizontally polarizedlog-periodic curtains 21L and 22U designed and arranged in such a mannerin the antenna structure that maximum gain is achieved for a givenantenna size. The lower curtain 21L and the upper curtain 22U arestacked vertically and arrayed with respect to a common apex such asindicated in FIGS. 2 and 3 with, however, the curtains truncatedarbitrarily and fed by a balanced feed section 23. Maximum broadbandgain is achieved by virtue of spacing the broadband log-periodiccurtains 21L and 22U apart and with respect to ground so as to achievethe optimum spacing of the curtain phase centers in height and also bypositioning of the curtain phase centers in substantially the samevertical line (or alternatively, making the array radiation phase fronta vertical line by retarding the phase of the upper curtain with respectto the lower). This phase shift is obtained on a broadband basis withoutrequiring special phase shifting devices in the antenna 20 with the twobay curtains 21L and 22U being at angles 32 and 47, respectively,relative to the ground plane from a common apex ground point. The rearmost end of the curtains 21L and 22U are mounted on towers 24 and 25 andthe ground apex end of the curtains 21L and 22U are anchored in placewith catenary end connections to concrete ground anchor pads 26 and 27.Further, a center concrete anchor pad 28 has a guy 29 connection to anantenna apex end post 30 mounting balun feed system 23 and havingadditional guy connections to the feed system 23 and the forward centerof the two bay curtains 21L and 22U. The two bays of the two curtains21L and 22U array are fed in a balanced manner without the exitation ofa high and/or lossy ground return current in the vicinity of the baluntransformer 31. The towers 24'and 25 that are mounted on concrete groundsupport pads 32 and 33 are each provided with three two wire guy wirepairs 34L and 34U, 35L and 35U, 36L and 3611, 37L and 37U, 38L and 38U,and 39L and 39U connected to the towers 24 and 25, respectivelysubstantially at the locations of curtains 21L and 22U connections,respectively therewith and extend to duplicate concrete ground guy wirepads 40, respectively. A working embodiment of this invention covering afrequency range of approximately 8 through 24 MHz gives substantially a15:1 DB1 gain at effectively a 15 elevation angle that is quite suitablefor long range HF signal propagation in the order of 1,5000 miles in anantenna structure with VSWR to frequency of less than 2 to 1 over theentire operational frequency range.

The antenna 20 is an array of two triangular tooth log-periodic antennabays that are horizontally polarized with the bays inclined over theground at angles of 32 and 48, respectively, and extending from the areaof a truncated feed point approximately 9 feet above ground, as shown inFIG. 4, to the towers 24 and 25 spaced at approximately 90 feet andextending from the ground to a height of approximately 150 feet.Referring also to FIGS. 5, 6, and 7, each of the bay curtains areequipped with radiating tooth elements 42U through 60U in the upper baycurtain 22U, and 42L through 61L in the lower bay curtain 21L. Tooth 60Uof upper bay curtain 22U is a truncated tooth as opposed to all theother teeth thereof being triangular radiating element teeth with atruncating crossover connective line 62U to a rear radiating elementline 63U. Line 63U extends from the element 62U to connection with thecenter feed line 41U and further to end termination connection with aninsulating jumper 64U with the conductive jumper line 62U and the endtermination connection with jumper 64U being at the limits of a 17 atangle. The 17 angle for the upper bay curtain 22U is defined byradiating element tooth tip ends and also by the outer lines 65 and 66of the upper bay curtain 22U three wire feed. The upper bay curtainthree wire feed with the lower bay curtain 21L three wire feed withouter feed wires 67 and 68 and center fee wire 41L and the respectivetriangular feed sections 69 and 70, respectively connected to outputlines 71 and 72 of balun 31, provide a balanced feed for the two baycurtain antenna 20. It is significant that outer feed wires 67 and 68are tapered at, and that the radiating element tooth 42L through 61Lends of the lower bay curtain 21L define an a angle of 23 an appreciablylarger angle than the 17 (1 angle of the upper bay curtain 22U.

Radiating elements and feed lines are made of stranded Alumoweld(aluminum covered steel) cables. The lower and upper cantenaries 73L and73U and 74L and 74U, extended, respectively, from concrete ground anchorpad 26 to tower 24 and from concrete ground anchor pad 27 to tower 25 inorder to support the lower and upper bay curtains 21L and 22U, are madeof Alumoweld cables that are broken with insulators 75 to preventdistortion of the antenna radiation pattern. Jumpers from the radiatingelement tip ends to the catenaries such as jumpers 76, 77, and 78 aremade of glass reinforced polyester rods compounded with titanium dioxideto resist ultra violet radiation. The feed to the antenna is through a50 ohm unbalanced coax line 79 connected to radio equipment (not shown)to balun 31 having a two line 71 and 72 balanced output that with thesix wire transmission line shown for a particular antenna built inaccord herewith is a 235 ohm balanced transmission line. With thisbalanced transmission line feed the lower bay triangular feed portion is3.5 feet long and the three wire transmission line section with wire 67is 14 feet long, while in the transmission line feed to the upper bay,the triangular feed section 69 is 3.37 feet long and the transmissionline section with line 65 is 20 feet long.

The larger, lower frequency end triangular radiating elements 57L, 58L,59L, and 60L of lower curtain bay 21L are provided with outer end tocenter feed line 41L connective lines 80, 81, 82, and 84, respectively.Alumoweld extensions 85, 86, 87, and 88 of the wires 80, 81, 82, and 84,broken with insulators, interconnect the center feed line 41L and thecatenaries 73L and 74L, respectively, for center feed line 41L andradiating element support. In like manner, tooth end to center feed line41U wires 89, 90, and 91 and Alu moweld jumpers, broken with insulators,92, 93, and 94 are extensions to catenaries 73U and 74U, respectively,provided in the upper curtain bay 22U.

The requirement in HF communications for antenna systems having goodradiation patterns and input impedance characteristics that areessentially frequency independent has resulted in the design of logperiodic antennas. Generally, the geometry of log-periodic structures isso chosen that the electrical properties repeat periodically with thelogarithm of the frequency and the operational bandwidth may bearbitrarily large by proper extension of the geometry of the structure.If the defining parameters of the antenna are adjusted so that thevariation over any one period is relatively small, then the variationwill be small over all periods with frequency independence being therebyobtained. The log-periodic antenna of finite length operates in anessentially frequency independent manner over a finite range offrequencies that depends primarily on the lengths of the longest andshortest radiating elements. The low frequency cut-off occurs when thelongest element is approximately one-half wavelength long/At anyfrequency between cut-off frequencies, the antenna currents are largestin the elements that are approximately one-half wavelength at theexcitation frequency with these elements contributing most of theradiation and forming the most active region of the antenna.

Applicants antenna is formed with generally horizontal elements in therespective array curtain bays with length and spacing determined bylog-periodic principles. The arrays produce a horizontally polarizedunidirectional beam radiated in the direction of the shortest elements.In each of the triangular toothed logperiodic antenna bays the teeth arespaced along the center feed line in log-periodic progression. Thespaces between teeth get larger as the distance from the apex isgreater. The ratio of the length of the adjacent similar teeth is suchthat the teeth are longer as the distance from the apex gets greater.This occurs in such a way that the tips of the radiating elementsdescribe a constant angle with the apex being common to the apex of thetwo curtain bays. These properties are known as the 7 ratio and atangle, and are the basic properties of a log-periodic antenna thataccount for the constant gain and impedance characteristics that a goodlog-periodic antenna will have over a broad range of frequencies.

In the subject antenna, it is significant that while each bay has thesame 1' ratio that the lower curtain bay has a wider at angle than theupper curtain bay. This advantageously allows the longest elements ofeach curtain bay to be located substantially directly vertically inline. Structural advantages inherent in this a angle variation may beappreciated by considering a structure with at angles equal in upper andlower array curtain bays so that a much greater tower height would havebeen necessary to keep the same angles of inclination since the lowerbay would have its longest element much behind the longest element ofthe upper curtain bay. Further, with an antenna sealed for the same lowfrequency limit as with the new antenna herein described and claimed thetower height reduction achievable using the new structure isapproximately 37 percent. In order to understand this distinctionbetter, consider that if the array curtains were identical and arrayedto a common apex on the ground the curtain phase centers would lie onthe arc of a circle whose center is at the array apex. This means thatthe lower phase center is closer to any vertical line to the rear of thearray than is that for the upper curtain. If the vertical linerepresents one of the rear supporting towers for the antenna a towerheight is given by X sine A where A is the angle of the upper curtainwith respect to ground and X is the distance that the tower is locatedaway from the apex. For a fixed A, X is determined by the lower curtainbecause of its smaller angle with respect to the ground. Scaling thelower element to obtain phase shift has the effect of increasing thetower height even more. It is obvious, then, that if the curtains couldbe designed so as to position the phase centers (and elements of equallengths) of the curtains in a vertical line (i.e., directly above andbelow one another) that X would be a lesser distance and so, the towerheight would be less.

Applicants HF antenna uses the ground to help form the desired radiationpattern with it being necessary that a relatively smooth area be inexistence where ground reflection occurs. Further, height of buildingsnear the reflection area must be limited so as not to block the groundreflected rays. Actually, the optimum antenna height for a given angleof radiation is with reference to FIG. 8 h (M4 Sine A) with the distanced from the ground point under the active center of the antenna to thereflection point being d (h /Tangent A). Actually, reflections occurover an area instead of just at a single point such as indicated by FIG.9 with the area over which reflections occur being defined by theconcept of a Fresnel zone. This Fresnel zone ground area is ellipticallyshaped with the distance to the far edge of the ellipse being d(h/Tangent A) and the distance the nearer edge being d (h/Tangent A).Further the width of the ellipse is W= 5.66 h. The subject antenna hasan effect takeoff angle equal to 15 and equivalent height of 0.965wavelengths. The following table summarizes dimensions and values withrespect to the reflection area for the antenna with respect to fourdifferent operationalfrequencies.

unidirectional broadband HF antenna 20 has VSWR to frequency in MHzcharacteristics from a 50 ohm unbalanced coaxial cable input linethrough the balun to 235 ohm balanced transmission such as shown in FIG.10 and not exceeding approximately 2.0 to 1 VSWR at any place over thefrequency range of operation. The elevation H plane patterns areadvantageously quite good with the elevation angle for the main lobebeing at substantially 15 through the frequency range of operation suchas illustrated by the elevation l-l plane patterns for the antenna at HMHz, 16 MHz, and 20.5 MHz by the FIGS. l1, l2, and 13, respectively.Furthermore, the E plane pattern remains much the same through thefrequency range of operation of the antenna with the E plane azimuthplane radiation patterns optimal for unidirectional electromagneticsignal propagation such as shown for 8 MHz, 13 MHz, and 22.5 MHz inFIGS. 14, 15, and 16, respectively.

Whereas this invention is herein illustrated and described with respectto a single specific embodiment thereof, it should be realized thatvarious changes may be made without departing from the essentialcontributions to the art made by the teachings hereof.

We claim:

1. In a unidirectional broadband horizontally polarized HF antennaoperational through a substantial portion of an 8 MHz to 24 MHzfrequency range: an upper log-periodic curtain bay array; a lowerlogperiodic curtain bay array; antenna mounting means mounting saidupper and lower log-periodic curtain above a ground plane in verticallystacked relation and arrayed with respect to a common projected apexapproximately at the ground plane; said lower and upper bays havinghigher frequency smaller ends toward said common projected apex andhaving lower frequency larger ends; said antenna mounting meansincluding rear tower means connected to and mounting the larger lowfrequency ends of said lower and upper bays with the upper bay slantedat a materially steeper angle relative to the ground plane than thelower bay; balanced transmission line feed means located at the apex endof said lower and upper bays feed connected to said lower and upperbays; and with the log-periodic aangle of the lower bay being materiallygreater than the logperiodic or angle of the upper bay so that the lowfrequency large ends of said lower and upper bays are substantially invertical alignment.

2. The unidirectional broadband horizontally polarized HF antenna ofclaim 1, wherein both said upper and lower bay arrays employsubstantially the same log-periodic 1' ratio.

3. The unidirectional broadband horizontally polarized HF antenna ofclaim 2, wherein both said upper and lower bay arrays are truncated atthe apex ends; and an antenna feed system including an unbalancedcoaxial line feed connected to a balun having balanced outputconnections through said balanced transmission line feed means to saidupper and lower bay arrays.

4. The unidirectional broadband horizontally polarized HF antenna ofclaim 3, wherein said balanced transmission line feed means includes twothree-wire transmission line sections one connected, respectively, toeach of said upper and lower bay arrays.

5. The unidirectional broadband horizontally polarized HF antenna ofclaim 4, wherein each of said three-wire transmission line sectionsincludes outer side wires substantially in line with and extending alongthe at angle sides of the respective bay arrays to feed connection atthe apex end of the antenna array.

6. The unidirectional broadband horizontally polarized HF antenna ofclaim 5, wherein each of said three-wire transmission line sectionsincludes a center wire extending the length of the the respective bayarray and electrically feed connected to all radiating elements of thearray.

7. The unidirectional broadband horizontally polarized HF antenna ofclaim 6, wherein each of said upper and lower bays is an array oftriangular tooth radiating elements.

8. The unidirectional polarized HF antenna of claim 7, wherein someteeth of each array include tooth end to feed center wire connectivewires.

9. The unidirectional broadband horizontally polarized HF antenna ofclaim 5, wherein the lower bay array and the upper bay array areinclined over the ground plane at approximately 32 and 48, respectively.

10. The unidirectional broadband horizontally polarized HF antenna ofclaim 9, wherein the a angles of the lower bay array and the upper bayarray are substantially 23 and 17, respectively.

11. The unidirectional broadband horizontally polarized HF antenna ofclaim 10, wherein said rear tower means includes two towers; each ofsaid upper and lower bay arrays include opposite side catenariesconnected to said towers at the rear of the antenna and to ground anchorpads at the apex end of the antenna structure.

12. The unidirectional broadband horizontally polarized HF antenna ofclaim 11, wherein the upper bay array is connected to the two towers atapproximately 150 feet above the ground plane; and the lower bay arrayis connected to the two towers at approximately feet above the groundplane.

13. The unidirectional broadband horizontally polarized HF antenna ofclaim 12, including balun mounting means supporting the balun with thebalun balanced output connections approximately 9 feet above the groundplane.

14. The unidirectional broadband horizontally polarized HF antenna ofclaim 13, wherein said catenaries are conductive metal cables brokenwith insulators along their lengths to prevent distortion of antennaradiation pattern.

broadband horizontally

1. In a unidirectional broadband horizontally polarized HF antennaoperational through a substantial portion of an 8 MHz to 24 MHzfrequency range: an upper log-periodic curtain bay array; a lowerlog-periodic curtain bay array; antenna mounting means mounting saidupper and lower log-periodic curtain above a ground plane in verticallystacked relation and arrayed with respect to a common projected apexapproximately at the ground plane; said lower and upper bays havinghigher frequency smaller ends toward said common projected apex andhaving lower frequency larger ends; said antenna mounting meansincluding rear tower means connected to and mounting the larger lowfrequency ends of said lower and upper bays with the upper bay slantedat a materially steeper angle relative to the ground plane than thelower bay; balanced transmission line feed means located at the apex endof said lower and upper bays feed connected to said lower and upperbays; and with the log-periodic Alpha angle of the lower bay beingmaterially greater than the log-periodic Alpha angle of the upper bay sothat the low frequency large ends of said lower and upper bays aresubstantially in vertical alignment.
 2. The unidirectional broadbandhorizontally polarized HF antenna of claim 1, wherein both said upperand lower bay arrays employ substantially the same log-periodic Tauratio.
 3. The unidirectional broadband horizontally polarized HF antennaof claim 2, wherein both said upper and lower bay arrays are truncatedat the apex ends; and an antenna feed system including an unbalancedcoaxial line feed connected to a balun having balanced outputconnections through said balanced transmission line feed means to saidupper and lower bay arrays.
 4. The unidirectional broadband horizontallypolarized HF antenna of claim 3, wherein said balanced transmission linefeed means includes two three-wire transmission line sections oneconnected, respectively, to each of said upper and lower bay arrays. 5.The unidirectional broadband horizontally polarized HF antenna of claim4, wherein each of said three-wire transmission line sections includesouter side wires substantially in line with and extending along theAlpha angle sides of the respective bay arrays to feed connection at theapex end of the antenna array.
 6. The unidirectional broadbandhorizontally polarized HF antenNa of claim 5, wherein each of saidthree-wire transmission line sections includes a center wire extendingthe length of the the respective bay array and electrically feedconnected to all radiating elements of the array.
 7. The unidirectionalbroadband horizontally polarized HF antenna of claim 6, wherein each ofsaid upper and lower bays is an array of triangular tooth radiatingelements.
 8. The unidirectional broadband horizontally polarized HFantenna of claim 7, wherein some teeth of each array include tooth endto feed center wire connective wires.
 9. The unidirectional broadbandhorizontally polarized HF antenna of claim 5, wherein the lower bayarray and the upper bay array are inclined over the ground plane atapproximately 32* and 48* , respectively.
 10. The unidirectionalbroadband horizontally polarized HF antenna of claim 9, wherein theAlpha angles of the lower bay array and the upper bay array aresubstantially 23* and 17*, respectively.
 11. The unidirectionalbroadband horizontally polarized HF antenna of claim 10, wherein saidrear tower means includes two towers; each of said upper and lower bayarrays include opposite side catenaries connected to said towers at therear of the antenna and to ground anchor pads at the apex end of theantenna structure.
 12. The unidirectional broadband horizontallypolarized HF antenna of claim 11, wherein the upper bay array isconnected to the two towers at approximately 150 feet above the groundplane; and the lower bay array is connected to the two towers atapproximately 90 feet above the ground plane.
 13. The unidirectionalbroadband horizontally polarized HF antenna of claim 12, including balunmounting means supporting the balun with the balun balanced outputconnections approximately 9 feet above the ground plane.
 14. Theunidirectional broadband horizontally polarized HF antenna of claim 13,wherein said catenaries are conductive metal cables broken withinsulators along their lengths to prevent distortion of antennaradiation pattern.